This invention is concerned with a self-centering bore arbor device to be used for mounting and aligning targeting scopes on shotguns.
Among those in the firearms community, it is becoming increasingly common to mount targeting scopes on shotguns and rifles. After being mounted on a gun, the crosshairs of the scope must be aligned with the ammunition trajectory. This is usually accomplished in one of two ways: Shooting ammunition at a target and then trying to estimate in which direction to adjust the crosshairs or the scope to bring the parallax of the scope in line with the ammunition trajectory. This method is time consuming and costly due to the amount of ammunition that must be expended. A second method is to use a bore scope, which is mounted on a bore arbor pin extending from a bore arbor device inserted into the bore of the gun, to prealign the parallax of the targeting scope with the intended trajectory of the ammunition. This is a much simpler and more economical approach.
Bore scopes have been used primarily on rifles, because a rifle bore cross section is circular of essentially constant diameter, and therefore, a simple cylindrical pin or shaft, which fits firmly into the bore of the rifle, can be used to mount the bore scope. However, until recently, bore scopes were not used on shotguns because shotguns have a tapering muzzle or choke which presented an obstacle to the firm seating of the bore arbor and the accurate alignment of bore arbor scope. Several devices have now been proposed to mount bore scopes on shotguns with varying degrees of success, and they are usually complex and costly.